Prostaglandins are compounds which have diverse physiological actions such as a powerful action in suppressing blood platlet aggregation, action in reducing the vasodilation blood pressure, action in suppressing gastric acid secretion, smooth muscle contraction action, cell protection action, and diuretic action and is useful for the treatment or prevention of myocardial infarct, cardiac angina, arteriosclerosis, hypertension, duodenal ulcers, induced parturition, abortion, etc.
On the other hand, in recent years, there has been a tendency toward an increase of skin ulcers, in particular, the decubitus ulcers known commonly as bedsores, along with the higher age of the subjects being treated for various ailments. For example, about 5% of the approximately 12 million senior citizens in Japan today, or 600,000 people, are bed-ridden. These people are said to suffer from decubitus ulcers at a high frequency. In the past, the treatment for skin ulcers, including decubitus ulcers, consisted of improvement of local conditions using antibiotics, antibacterial agents, ointments containing enzymes etc., skin cleaning solutions, or water absorbing polymer powders, wound covering agents, etc. These have been tried along with removal and mitigation of the pressure on the diseased sites, surgical debridement for removal of the destroyed tissue, treatment of systemic conditions by transfusions, intraintestinal nutrition, and IVH, but these treatments still cannot be said to be sufficiently effective. On the other hand, attempts have been made to apply prostaglandin E, prostaglandin F, and prostaglandin I.sub.1 transdermal preparations to skin ulcers, including decubitus ulcers, for the purpose of improvement of skin ulcers by application to local areas, but the stability of the main medication, the release of the main medication from the ointment, the stimulus to the skin, and the efficacy have not always necessarily met clinical requirements.
Natural prostacyclin, however, is a local hormone produced mainly by the hemangioendothelium in the body. Attempts have been made to make use of its powerful physiological activity, for example, its activity in suppressing aggregation of blood platlets, its vasodilation activity, etc. to use the same as a direct pharmaceutical (P. J. Lewis, J. O. Grady, Clinical Pharmacology of Prostaglandin). Natural prostacyclin, however, contains an enol-ether bond which is extremely easily hydrolyzed in the molecules, and therefore, easily loses its activity under neutral or acidic conditions. Accordingly, it cannot be said to be a desirable compound as a pharmaceutical due to its chemical instability. Therefore, intensive research has been carried out on synthesizing a synthetic prostacyclin which has a similar physiological activity as natural prostacyclin and is chemically stable (Synthesis, 1984, 449). The present inventors succeeded in synthesizing the prostacyclin analogs, which are 9(O)-methano-.DELTA..sup.6(9.alpha.) -prostaglandins I.sub.2 (isocarbacyclin), derivatives which are sufficiently satisfactory in the chemical stability, by replacing oxygen atoms at the 6(9.alpha.)-position of prostacyclin with the methine group (--CH.dbd.) (see Japanese Unexamined Patent Publication (Kokai) No. 59-210044). This derivative has physiological activity, such as a powerful action in inhibitory effect on aggregation of blood platlets and an action in reducing the blood pressure, comparable with natural prostacyclin and is useful for cardiovascular system (see Japanese Unexamined Patent Publication (Kokai) Nos. 59-210044 and 61-197518).